Prior laser shutter designs have used moving reflective mirrors to redirect the beam to an absorbing region. Moving mirrors deflect beams to a geometrical surface morphology and atomic absorption centers. This works well at low irradiance and low fluence (energy density, J/cm2), but requires highly sophisticated and expensive mirrors tailored for individual wavelengths. Moreover, as the power increases, pulse width time shortens, or beam diameter is reduced, the mirrors cannot provide high laser induced damage threshold (LIDT) for broadband use. Hence, many wavelength-specific mirrors must be used for various applications. Additionally, any contamination present on the mirror surface can generate a catastrophic failure.
Moving mirrors need extreme mechanical mounting protection for fracture safety. Most mechanical movement systems use bearings with only point or line contact, not surface contact, so there is virtually no heat flow. Flexure systems have no significant thermal cross-section.
Water-cooled (umbilical) pucks with ceramic (SiC, AlN) coating have been used for optical absorption. Large volume, doped glasses have limited absorption times due to heat build-up. Very intense laser light sources would quickly obliterate any glass or absorbing film structure. Additionally, sacrificial surfaces can contaminate via particles and outgassing.
Desired properties of a laser shutter adapted for high intensity laser pulses include a broadband range of operation so that one device works with most or all of the available laser wavelengths (typically 150-11000 nm) and avoid needless specificity. The shutter should be able to handle high irradiance (pulsed or cw; 1 mm diameter or smaller beams) without limitations on exposure to the beam, and have very high laser induced damage threshold (LIDT), so that the shuttered beam produces no contamination or any drill-through of the device material and no material is liberated from the shutter device. The shutter should be able to manage the heat load (typically in 50-100 W range), so the unit will be largely insensitive to any surface contamination films. It should not outgas and be bakeable to remove organics, i.e. eliminate or limit polymers. There should be no back reflection and minimized backscatter to the laser source. The failsafe is a closed state and there should be no leakage of the beam energy when closed. The shutter needs to remove heat and still have a moving element, with low shock and vibration when moving between open and closed positions. A small package and simple electronic drive, as well as commercially-available components and low cost are preferred and there should be no extreme supplier constraints.